20.7 Input Events

The Emacs command loop reads a sequence of input events that
represent keyboard or mouse activity, or system events sent to Emacs.
The events for keyboard activity are characters or symbols; other
events are always lists. This section describes the representation
and meaning of input events in detail.

— Function: eventp object

This function returns non-nil if object is an input event
or event type.

Note that any symbol might be used as an event or an event type.
eventp cannot distinguish whether a symbol is intended by Lisp
code to be used as an event. Instead, it distinguishes whether the
symbol has actually been used in an event that has been read as input in
the current Emacs session. If a symbol has not yet been so used,
eventp returns nil.